Many subwoofers have two kinds of input: a single jack marked LFE and a pair marked Line In L/R (and sometimes speaker-level terminals too). They look similar but behave differently. Using the wrong one is a common cause of thin or boomy bass.
- Using an AV receiver or soundbar Sub Out? Use LFE. It bypasses the sub’s own crossover so the receiver’s bass management works properly.
- Using a stereo preamp or powered speakers? Use Line In L/R, and set the sub’s crossover yourself.
- Stereo amp with no sub output? Use speaker-level inputs.
What the LFE input does
LFE (low-frequency effects) inputs send the signal straight to the sub’s amplifier, skipping its internal low-pass filter. That’s what you want with a receiver, because the receiver has already filtered the signal at your chosen crossover (usually 80 Hz). If the sub also filtered it, the two filters would stack and cut too much around the crossover point.
What line inputs do
Line In L/R passes through the sub’s own crossover, so you control where the sub stops playing with its dial or app. That’s right for stereo systems where nothing else is filtering the bass. With two inputs, the sub sums left and right together.
| Your source | Input to use | Sub’s crossover setting |
|---|---|---|
| AV receiver Sub Out | LFE | Bypassed automatically |
| Soundbar Sub Out | LFE (usually) | Bypassed |
| Stereo preamp / pre-out | Line In L/R | Set to match speakers |
| Powered speakers with sub out | Line In or LFE (check manual) | Depends on speakers |
| Amp speaker terminals | Speaker-level | Set to match speakers |
What if my sub has no LFE input?
Use one of the line inputs (either channel) and turn the sub’s crossover to its maximum setting. That effectively takes it out of the way.
Should I use a Y-splitter into both line inputs?
Some people split the receiver’s sub output into both L and R line inputs to get about 6 dB more signal into the sub. It doesn’t change sound quality, but it can help a sub’s auto-standby stay awake. See auto-standby problems. Remember to set the sub’s crossover to maximum if you do this.